I have a friend who abuses amphetamines and I have repeatedly seen the dopaminergic effects played out in a manner that perfectly mimics my bipolar changes. When the friend is "speeding" it's just like my "mania" episodes; when they run out of the amphetamines, they act and look like my "depressive" side.
The mania is pretty self-explanatory, exhibiting increased activity, speaking very rapidly, twitching, racing thoughts, and anorexia. With the withdrawal from the drug they will sleep, sometimes for days, talk and process information very slowly and dully, and eat (mostly carbohydrates and so-called comfort food).
Researchers should think outside the box in this particular subject and take advantage of the untapped resources available. Also interesting would be a longitudinal study investigating the long-term effects of amphetamines upon the whole dopaminergic system in drug users to correlate their decreasing functionality with that of Parkinson's patients who lose their capabilities naturally instead of chemically.